Some interesting remarks about leaf shutters and some designs I had not
heard about . . . but make practical sense and have mechanical simplicity.
The real shutter and optics techies know more about application details
than I do.
I have been under the impression (perhaps mistaken :-O ) the issue with
pushing leaf shutters beyond 1/500th is whether the shutter blades can move
fast enough for the high shutter speed. Depending on how close the leaf
shutter is to the diaphragm . . . isn't there risk of vignetting if the
attempted shutter speed is very high compared to how fast the blades move,
especially at the wider apertures? Less exposure at the outer portion of
the image cone and more at the center? Risk (or effect) goes up as shutter
is moved further from diaphragm?
Hoping for some further enlightenment.
-- John
At 03:27 4/17/00 , you wrote:
> jlind@xxxxxxxxxxx writes:
>
><< The practical limit on a leaf shutter is about 1/500th. Shutter
> speeds faster than 1/500th can have problems with producing an even
> exposure across the film plane. >>
>
>John,
> I don't know what is used in the XA but.. If it is a leaf shutter
>it has a circular opening so at high speeds it just has a variable F-stop as
>the blade travel time becomes a significant part of the exposure time. Thus
>the exposure remains even across the film plane even if it is slow. In some
>small auto only cameras the diaphragm is the shutter and it only opens part
>way so the travel time is less significant at small f-stops. (Thus program
>mode is a good fit :small f-stop+high speed) Similarly if the shutter and
>diaphragm are placed close together. The distance that the blades have to
>travel in an XA is also probably much shorter than say a large format leaf
>shutter that struggles to get to 1/500sec. As an aside, some cheap auto
>cameras have terrible bokeh as the combined shutter/diaphragm has only two
>leaves with aa approximately rectangular shaped opening.
>
>Regards,
>
> >>>Tim Hughes<<<
>
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